Plastic coating on bisque enamel



Oct. 27, 1964 D. H. KOHNKEN Filed April 7, 1960 PLASTIC COATING 0N BISQUE ENAMEL.

INVENTOR a/v/n a ff /fo HN/rE/v ATTORNEYS United States Patent O 3,154,426 PLASTIC CATING N BESQUE ENAMEL Donald H. Kohnlken, Baltimore, Md., assigner, by mesne assignments, to The Giidden Company, Cleveland, (Ehio, a corporation of Ohio Filed Apr. 7, i969, Ser. No. 20,525 9 laims. (Ci. 117-4) This invention relaties to a method for treating bisque enamel, i.e., unired porcelain enamel, to improve body and adherence characteristics thereof. In particular, the invention relates to a process for treating bisque enamel applied to metal whereby deformation of tne metal can be carried out with no adverse effect on the bisque enamel coating.

Porcelain enamel has been used for many years and for many purposes. A primary feature of a porcelain enamel coating on metal, other than appearance, is the protection afforded, particularly against high temperatures, corrosion, weathering, and the like. These protective characteristics make it desirable to apply porcelain enamel to articles which are subjected to conditions of high ternperatures, corrosion, and the like.

However, one drawback that has been encountered in the past is with regard to metal articles having relatively intricate shapes, as for example an automobile mufiier. Fabrication of such an article with a porcelain enamel coating thereon can follow one of two courses. The article can first be fabricated and porcelain enamel thereafter applied to the fabricated article. Alternatively, the article can be shaped and joined from'metal sheets to which a porcelain enamel coating has previously been applied.

The first of these alternatives has been found impractical in many cases, because of the difficulty encountered in achieving a uniform application of bisque enamel prior to firing. Specifically, in an article such as an automobile mufer, which has hidden recesses, bae arrangements, and the like, the frit material is inaccessible thereto after fabrication. The result is a porcelain enamel coating on parts of the muffler leaving exposed other parts which remain vulnerable to the adverse effects noted heretofore.

The second alternative has been equally impractical. If a porcelain enamel coating is first applied to metal and the metal then fabricated, the porcelain enamel will fracture during deformation of the metal and thus become inoperative for its intended purpose. As a matter of fact, even if the bisque enamel is first applied, the article fabricated, and firing of the frit then carried out, the same problem is encountered, since the bisque enamel may flake off during the fabricating phase due to insufcient body and adherence characteristics.

The present invention has been delevoped for the purpose of making the second alternative procedure recited heretofore a more practical means for porcelain enamelling intricately shaped metal articles. Specifically, a frit material is applied to sheet metal following which an organic plastic material is added as a predominantly surface layer, yet permeating the bisque enamel and adhering to the metal substrate. Application of such organic plastic material has made possible the deformation of the metal substrate by stamping, bending, drilling, or shearing, yet without incurring fractures in the region where the metal is being so fabricated. Following fabrication, the organic plastic material is eliminated before or during the firing of the bisque enamel coating. The result is an excellent porcelain enamel finish on all treated surfaces of the fabricated article.

An ancillary advantage of the invention can be the elimination of all but the fabrication and firing steps in the article manufacturers plant. In other Words, the

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manufacturer can purchase rolls of sheet metal to which the bisque enamel and organic plastic material have already been applied. Thus, pickling, milling, spraying, and all enamelling operations other than firing can be carried out at the source of the sheet metal rolls, said source normally being better equipped for such operations.

With the above in mind, the primary object of this invention is to provide a method for treating bisque enamel to improve body and adherence characteristics thereof.

Another object of the invention is to provide a process for applying bisque enamel to a metal substrate whereby such metal substrate can be deformed without adversely affecting the bisque enamel coating.

A further object of the invention is to provide a process for treating bisque enamel to improve body and adherence characteristics thereof, comprising applying a coating of said bisque enamel to the surface of a substrate material, and thereafter applying an organic plastic material thereto, said organic plastic material capable of being burned out prior to maturing of said bisque enamel to a final porcelain enamel nish, thereby permitting deformation of the substrate material and bisque enamel coating without adversely affecting said bisque enamel.

An additional object of the invention is to provide a process for applying porcelain enamel to metal articles comprising applying a coating of bisque enamel to the surface of a base metal, thereafter applying an organic plastic material to the bisque enamel as to permeate the said bisque enamel and adhere to the base metal, fabricating a metal article from the said coated base metal, heating the fabricated article to burn out the organic plastic material and mature the bisque enamel to a final porcelain enamel finish, whereby fabrication of the coated base metal is carried out without adversely affecting said bisque enamel and the porcelain enamel nish resulting therefrom.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specic examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The organic plastic material used in the process described heretofore must meet certain basic requirements. These are:

(a) The material must be easily applied, by, for example, brushing, dipping, or preferably by spraying.

(b) The material must permeate the bisque enamel layer and adhere to the metal substrate.

(c) The material must dry rapidly in air.

(d) Following drying, the material must have good elasticity, be non-brittle and non-tacky.

(e) The material must be unaffected by normal temperatures and humidity.

(f) The material must be capable of burning out at moderately low temperatures. (Below the fusing range of the bisque enamel.)

(g) The material should be essentially ash free and should not in any stage react with or affect the bisque enamel, as for example, by bubbling or foaming.

A description of the optimum material would be one which readily penetrates the bisque enamel coating and adheres to the metal substrate, readily dries to non-brittle but non-tacky consistency, and readily burns out at a relatively low temperature without adversely affecting the final porcelain enamel coating.

Several different organic plastic materials have been found to be useful. Preferred are the acrylic ester resins, e.g. butyl, ethyl, and methyl methacrylates, such as Rohm and Haas Acryloids F10, B82, and B66, and Seymours 16-121, which are generally classied as polymers of esters of acrylic and methacrylic acids. The acrylic esters are normally used in solution with, for example, mineral spirits, toluol, or methanol, but an acrylic emulsion in water, such as Rohm and Haas Rhoplex AC-33, also is satisfactory, if the drying time of the organic vehicle is not overly extended. Solids content of from about to 60% by weight of composition is preferred for these acrylic emulsions and solutions.

Other organic materials which have been used successfully include hydroxyethyl cellulose (Union Carbide Various solvents can be used in conjunction with the foregoing organic plastic materials and in various ratios. Examples include water, lower alcohols (methanol, ethanol), esters (butyl acetate), ketones (acetone, methyl ethyl ketone), and mineral spirits (Esso Varsol). Water is preferred for the emulsions, but, again, includes a disadvantage of requiring extended drying time.

The amount of solvent used in forming the organic vehicle will depend, of course, upon the particular solvent and organic plastic material used with a preferred range being about 15 to 60% solids content by weight of composition. In any event, although the organic vehicle is a predominant surface layer, it must be capable of permeating the bisque enamel coating and adhering to the metal substrate in order to supply optimum body and adherence characteristics to said bisque enamel. This is normally accomplished by appropriate dilution of the organic plastic material with the solvent.

Reference is made to the flow sheet in the drawing with regard to the sequence of operation hereinafter described.

In actual operation, the bisque enamel coating is first appliel to the metal substrate. The amounts applied are conventional and well known to the art with a range of from 5 to 50 grams per square foot of metal substrate being typical. The composition of the bisque enamel is also conventional as, for example, frit (100 parts), clay (8 parts), SiO2 (5 parts), borax (0.5 part), MgCO3 (0.25 part), NaNO2 (0.125 part), bentonite (0.25 part), H2O (45 parts). Various metal substrates are contemplated, depending upon the article being fabricated. Typically, a low-carbon, low-metalloid, cold-reduced steel is used.

The organic material is thereafter applied, preferably by spraying and in amount of about 2 to 25 grams by dry weight per square foot of bisque enamel being treated, depending upon the type and make up of the organic vehicle used.

Before firing the bisque enamel, various fabrication steps are carried out on the metal to yield the final product. Thereafter, the fabricated article can be directly fired at temperatures of from about 1000 F. to 1600 F. for a time of from about 3 to 10 minutes, or first subjected to a preliminary heat treatment at temperatures of from about 500 F. to 800 F. for a time of from about 10 to 60 minutes, depending upon the type of organic vehicle used.

Most of the above noted organic plastic materials are capable of burning out during the firing operation. However, in the case of aqueous emulsions, and lacquers, particularly, cellulose acetate and nitrocellulose, a preliminary heat treatment during which the organic vehicle is burned out must be used before firing. This is necessary because of the rapid burning out rate of such organic vehicles which yields vapor interference that would adversely affect porcelain enamel during the actual firing step. In every case, the organic material is burned out before the bisque enamel matures into a final porcelain enamel coating.

My invention is more fully illustrated by the following examples.

Example I A sheet of 18 gauge enamelling iron was coated with bisque enamel in amount of l5 grams per square foot. The bisque enamel had a composition comprising frit parts), clay (7 parts), feldspar (8 parts), borax (0.625 part), MgCQa (0.125 part), bentonite (0.125 part), and water (45 parts). Thereafter an acrylic ester resin dissolved in mineral spirits (Rohm and Haas Acryloid F10), was brushed on the bisque enamel and allowed to air dry. The solids con-tent of the solution was 40% and sufficient of such was brushed on the bisque enamel as to permeate the latter and adhere to the metal substrate. For an iron sheet of one square foot, 20 grams by dry weight of acrylic ester resin were applied.

The coa-ted metal panel was then fabricated including stamping, bending, and shearing, following which firing of the bisque enamel was carried out at a temperature of l550 F. for a time period of 3 minutes. Before the bisque enamel matured into a final coating, the organic plastic was burned out as to leave an excellent porcelain enamel surface finish on all treated areas.

Example ll The procedure of Example I was carried out through the application of the organic plastic material. However, in this example, a water emulsied acrylic ester resin (Rhoplex AC-33) having a solids content of 30% was substituted for the acrylic ester resin solution. Following application of the emulsion by spraying (6 grams per square foot), and after the emulsion was air dried, and the fabrication steps carried out on the coated metal sheet, a preliminary heat treatment was conducted at 800 F. for a time period of 30 minutes to burn out the resin. Then, the fabricated sheet was further treated at a temperature of 1475 F. for 3 minutes during which the bisque enamel matured to a final porcelain enamel finish. The preliminary heat treatment was necessary because of the fact that the emulsion has a rapid burn out rate. If carried out at fusion temperatures, the rapid burn ou-t would generate vapors having adverse effect such as bubbling, foaming, and the like, on the final porcelain enamel finish.

Example III A sheet of 20 gauge enamelling iron was coated with bisque enamel in amount of 8 grams per square foot. The bisque enamel had a composition comprising frit (100 parts), clay (8 parts), SiOg (5 parts), borax (0.5 part), MgCO3 (0.25 part), NaNO2 (0.125 part), bentonite (0.25 part), H2O (45 parts). Thereafter polyvinyl acetate dissolved in methanol (Elvacet 60-05) was sprayed on the bisque enamel and allowed to air dry. The solids content of the solution was 30% and sufficient of such was sprayed on the bisque enamel as to permeate the latter and adhere to the metal substrate. For an iron sheet of one square foot, 2O grams by dry weight of polyvinyl acetate were applied.

The coated metal panel was then fabricated and fired at 1475 F. for a time period of 5 minutes to yield an excellent porcelain enamel surface finish on all treated areas.

Example IV The procedure of Example III was carried out through the application of the organic plastic material. However, in this example a nitrocellulose lacquer solution (Standard- Toch 154-C47) having a solids content of 30% was substituted for the polyvinyl acetate solution. Following application of the solution by spraying (4 grams per square foot), and after the solution was air dried, and the fabrication step carried out on the coated metal sheet, a preliminary heat treatment was conducted at 600 F. for a time period of 45 minutes to burn out the lacquer. Then, the fabricated sheet was further treated at a tempera-ture of 1375 F. for `8 minutes during which the bisque enamel matured to a final porcelain enamel finish.

Although preferred ranges of temperature, time, proportions, and the like have been set forth, broader ranges are many times contemplated. It must be understood that the invention is not limited to preferred ranges so long as the desired results are effected. The invention includes all variations and procedures covered by the appended claims and their equivalents.

I claim:

1. A process for applying porcelain enamel to metal articles comprising applying a coating of bisque enamel to the surface of a base metal and drying said bisque enamel coating, thereafter applying an organic plastic material to the bisque enamel as to permeate the said bisque enamel and adhere to the base metal, said organic plastic material being one which readily penetrates the bisque enamel coating and adheres 'to the base metal, which readily dries to non-brittle yet non-tacky consistency, and which readily burns out at a relatively low temperature without adversely affecting the final porcelain enamel finish, thereafter fabricating a metal article from the said coated base metal, heating the fabricated article to burn out the organic plastic material and mature the bisque enamel to a final porcelain enamel finish, whereby fabrication of the coated base metal is carried out without adversely affecting said bisque enamel and the porcelain enamel nish resulting therefrom.

2. A process as claimed in claim 1 wherein the organic plastic material is selected from the group consisting of acrylic ester resins, hydroxyethyl cellulose, polyethylene glycol, polyvinyl acetate, alkyd resins, lacquers, polymers of ethylene oxide, and limed wood rosm.

3. A problem as claimed in claim 1 wherein the 0rganic plastic material is combined with a compound selected from the group consisting of water, alcohols, esters, ketones, and mineral spirits in the amount of about 15 to 60% organic plastic solids by weight of total composition.

4. A process as claimed in claim 1 wherein the organic plastic material is applied in an amount of about 2 to 25 grams by dry weight per square foot of bisque enamel being treated.

5. A process as claimed in claim 1 wherein said fabricated article is heated to a temperature of from about 1000 to 1600 F. for a time of from about 3 to 10 minutes.

6. A process as claimed in claim 1 wherein the fabricated article is subjected to preliminary heat treatment of from about 500 F. to 800 F. for a time period of from about 10 to 60 minutes to burn out the organic plastic material, following which the fabricated article is further heated at a temperature of from 1000 to 1600 F. for a time period of from about 3 to 10 minutes whereby the bisque enamel is fired and matured to a final porcelain enamel finish.

7. A process as claimed in claim 6 wherein the organic plastic material is an aqueous emulsion.

8. A process as claimed in claim 6 wherein the organic plastic material is a lacquer.

9. A process as claimed in claim 1 wherein the organic plastic material is applied by spraying.

References Cited in the file of this patent UNITED STATES PATENTS 1,230,958 Warga June 26, 1917 2,682,480 Andrews June 29, 1954 2,848,794 Roth Aug. 26, 1958 2,892,734 Hoffman lune 30, 1959 2,935,422 Chester et al. May 3, 1960 2,985,547 Luks May 23, 1961 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3, 154,426 Oct-ober 27, l964 Donald Hf. Kohsnken lt is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column l,l line 9, for "relaties" read relates column 6Y line l, for "problem" read process signed and sealed this 6th day of April 1965,

(SEAL) Attest:

ERNEST W. SWDER EDWARD J BRENNER Attesting Officer Commissioner of Patents 

1. A PROCESS FOR APPLYING PORCELAIN ENAMEL TO METAL ARTICLES COMPRISING APPLYING A COATING OF BISQUE ENAMEL TO THE SURFACE OF A BASE METAL AND DRYING SAID BISQUE ENAMEL COATING, THEREAFTER APPLYING AN ORGANIC PLASTIC MATERIAL TO THE BISQUE ENAMEL AS TO PERMEATE THE SAID BISQUE ENAMEL AND ADHERE TO THE BASE METAL, SAID ORGANIC PLASTIC MATERIAL BEING ONE WHICH READILY PENETRATES THE BISQUE ENAMEL COATING AND ADHERES TO THE BASE METAL, WHICH READILY DRIES TO NONE-BRITTLE YET NON-TACKY CONSISTENCY, AND WHICH READILY BURNS OUT AT A RELATIVELY LOW TEMPERATURE WITHOUT ADVERSELY AFFECTING THE FINAL PORCELAIN ENAMEL FINISH, THEREAFTER FABRICATING A METAL ARTICLE FROM THE SAID COATED BASE METAL, HEATING THE FABRICATED ARTICLE TO BURN OUT THE ORGANIC PLASTIC MATERIAL AND MATURE THE BISQUE ENAMEL TO A FINAL PORCELAIN ENAMEL FINISH, WHEREBY FABRICATION OF THE COATED BASE METAL IS CARRIED OUT WITHOUT ADVERSELY AFFECTING SAID BISQUE ENAMEL AND THE PROCELAIN ENAMEL FINISH RESULTING THEREFROM. 